The present invention relates to a non-slip surface which serves as a base for the insole of a shoe construction. More particularly, the present invention relates to a non-slip surface which provides a mechanical interlock for effectively holding a shoe insole in place.
In an attempt to understand the foot as a system, the various parameters which affect the function of the foot have been studied, particularly with regard to a weight bearing foot. The practical need for such knowledge lies in the fact that a true structural model of the foot is capable of providing a prediction of gait and the effects of a shoe on gait. By knowing, in advance, how a shoe would affect the performance of an athlete, for example, optimum shoes could be designed without the usual "cut and try" method of standard shoe development.
The traditional model of the foot provides for a one column, two-axis model which maintains that the foot under load is a rigid structure with a talocrural (ankle) axis and an apparent subtalar axis. The front of the foot is relatively rigid, but with only a multitude of small bone movements about the midtarses axes. The average direction of the effective axis under the ankle, called the subtalar axis, is said to be 42 degrees vertical and 16 degrees horizontal to the midline of the body, as measured by Inman, V. T., The Joints of the Ankle, The Williams & Wilkins Co., Baltimore, 1976. However, this theory does not hold up with regard to a weight bearing or loaded foot since, if the force due to body weight were to act on the single traditional subtalar axis, the foot would collapse mechanically.
It has now been determined that the foot is comprised of two columns and three axes. The lower, lateral column is basically a rigid base comprised of the Calcaneus, Cuboid, and the fourth and fifth metatarsals. The remainder of the foot, which is comprised of the navicular, the first, second and third cuneiforms and the first, second and third metatarsals, emanates from the talus at the talonavicular interface swinging in combination with the lower column inversion/eversion actions in what may be called the `subtalar joint axis`. But this articulation of what is called the upper foot column is only secondary to the true foot mechanism. The primary mechanical loading interface is on the lower, lateral column at the rear of the talus onto the calcaneus, the posterior talocalcaneal facet.
It has also been determined that the foot operates differently under load than when it is passively manipulated such as a doctor would do in the office. This distinction helps to explain previous misconceptions as to how the foot works under load.
This new understanding has yielded a new structural model of the foot which has two separate columns, wrapped together with fascia, and three nearly orthogonal axes. The three axes are: (1) the talocrural (ankle) axis; (2) the talocalcaneal axis (formed at the facet between the talus and the calcaneus); and (3) the talonavicular axis (formed at the facet between the talus and the navicular bones).
It has been traditional in the past for shoe insoles to be either glued into a shoe or to be placed inside the shoe upper with only shoe irregularities and fabric texture to interlock with the soft undersurface of the insole insert. Thus in the past, the shifting and slipping of the insole within the shoe during use has been a common problem.
By the present invention, there is provided a non-slip base surface for a shoe insole in which a mechanical interlock between the base and the insole is used as the exclusive means for holding the insole in place. The insole base of the present invention provides a low volume, low profile molded pattern which penetrates the insole material and prevents shearing shifts. The present insole base can be molded directly onto the fabric of the upper material which forms the cover over the outsole or, alternatively, the pattern may be molded onto any suitable separate fabric sheet which can then be die cut to shape and permanently adhered to the bottom of the shoe.
Accordingly, it is an object of the present invention to provide a non-slip surface for a shoe insole based on mechanical locking as opposed to pure sliding friction or adhesives and stitching.
It is a further object of the invention to maximize interlock shear strength and to minimize material volume for an insole base, with the result that pattern directionality is related to dynamic shear forces and so that material and shape are related to properties of the insole.
It is another object of the invention to provide an insole base which is easily moldable to any shoe surface.
It is a further object of the invention to provide a permanent non-slip insole base which is effective for the life of the shoe.